Articular chondrocytes have a limited capacity for tissue repair, contributing to degenerative changes in articular cartilage, including osteoarthritis. One factor that is known to control the metabolic behavior of these cells is mechanical forces. However, the mechanisms by which chondrocytes sense and respond to mechanical forces are not well understood, Recent studies have suggested that the focal adhesion complex may serve as a mechanical signal transducer, through a process of cytoskeletal linkage reinforcement. The governing hypothesis of this project is that focal adhesion sites between the chondrocyte and its surrounding extracellular matrix serve as force transducers, converting mechanical signals into biochemical signals that may alter cellular function. To test this hypothesis, a novel experimental system based on a micromachined force sensing device will be used to study interactions between single isolated cells and single collagen fibers. This system will be used to execute the following specific aims: (1) Quantify the forces exerted by single isolated chondrocytes on individual collagen fibers; (2) Examine the assembly of focal adhesion sites under single collagen fibers using green fluorescence protein-labeled markers; (3) Examine the response of focal adhesions to static and dynamic mechanical forces applied through single collagen fibers. Determining the role of focal adhesions in mechanical signal transduction will lead to a greater understanding of the role of mechanical forces in both degeneration of articular cartilage in vivo and development of tissue engineered repair strategies in vitro.